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They came to the South Pole, enduring months of bitter cold, darkness, and isolation, to peer at the galaxy’s center through clear, dry skies. And in December, they – scientists from the Harvard-Smithsonian Center for Astrophysics (CfA) – declared “mission accomplished.”

After 11 years, the Antarctic Submillimeter Telescope and Remote Observatory, AST/RO, was dismantled last fall. The 1.7- meter telescope was boxed up for transport and now sits on the snow, awaiting a decision on its next stop.

CfA scientist Antony Stark, the project’s principal investigator, said AST/RO confirmed theories about an enormous ring of interstellar gas in the galaxy’s center and helped explain why the Milky Way’s central black hole is less active than those at the center of other galaxies.

“We believe that the black hole is being starved of gas,” Stark said during a recent interview.

Stark explained that astronomers believe that every galaxy has a black hole at its center. Some of those galactic black holes appear very active. Though nothing can escape a black hole’s gravitational pull, many emit X-ray radiation, generated by gas that superheats as it falls into the black hole itself.

But the black hole at the center of the Milky Way is quiet. Thanks to AST/RO, Stark and other project scientists believe they know why.

Peering at submillimeter radiation coming in through the South Pole’s thin, clear skies, AST/RO scanned the center of the galaxy for interstellar gas, specifically carbon monoxide.

Carbon monoxide is among the most abundant of the 100 different molecules known to exist in interstellar space, Stark said, making it a useful indicator for the location of interstellar gas clouds.

Using measurements taken through AST/RO, scientists found an enormous gas ring surrounding the Milky Way’s center, confirming earlier theories of the ring’s existence.

Stark and other AST/RO scientists now believe that the Milky Way’s central black hole is prone to sporadic bursts of activity every 50 million years or so. That’s because the central gas ring is slightly unstable, according to AST/RO’s measurements.